1. Field of the Invention
This invention relates to semipermeable membranes of polyaryl ether sulfones having a high hydrophilicity which can be used in the filtration of water and a process for preparing the same.
2. Description of the Prior Art
As the materials for semipermeable membranes a large number of polymers are presently used. For example, cellulose acetates, polyacrylonitriles and polyamides are industrially produced as the materials for semipermeable membranes.
Also polyaryl sulfones which are used as an engineering plastics have now been employed as the materials for semipermeable membranes due to their good resistance to heat and chemicals. However, the hydrophilicity of polyaryl sulfones is low and accordingly, the semipermeable membranes of polyaryl sulfones have various disadvantages in the filtration of water due to their low wettability to water.
For example, in operating an filtration using an apparatus incorporated with semipermeable membranes, bubbles often get entangled in the apparatus. In case the semipermeable membranes have a low wettability to water, the bubbles adsorb on their surfaces and do not separate therefrom readily and easily, resulting in dead spaces which reduce the filtration rate of the apparatus. Further, the semipermeable membranes having a low wettability to water are easily dried upon exposure to air and as a result the water permeability tends to decrease.
The hydrophilicity and the water permeability of semipermeable membranes of polyaryl ether sulfone can be improved to some extent by introducing sulfonic groups into the aryl groups of the polyaryl ether sulfones (Journal of Applied Polymer Science, Vol. 20, page 1885, 1976). However, the hydrophilicity of the semipermeable membranes of the polyaryl ether sulfones which do not have such strongly acidic atomic groups, i.e., do not have any substituents in the aryl groups or only have non-dissociable substituents in the aryl groups is low and the contact angle of the surfaces of the semipermeable membranes to water is at least 70.degree..